The art of sampling molten metal and obtaining temperatures with thermocouples has developed significantly since the early 1960's In addition to various forms of sampling cartridges, sampling techniques and thermocouple lances, various improvements have been made in protecting the sampling vehicles or lances during immersion to provide sufficient immersion time to obtain a representative metal sample below the slag surface of the melt and obtain a representative bath temperature. In addition to protecting the immersion vehicle, there also is an interest in protecting the equipment operator who is taking the temperature or the sample from the splash of molten metal caused by boiling or combustion gases caused by disintegration of the sampler vehicle. The paperboard products employed to protect samplers will attain ignition or kindling temperatures but because of lack of oxygen will gasify rather than burn.
Various types of protective coatings have been employed. Wrappings of fiber coated paper have been used. The gasification or combustion of the paper causes some splash and boiling as the paper is consumed. A further protective coating employed in the art is a fiberglass tape wrapped over a coating of refractory cement. Fiberglass tape depends on its strength to prevent blowing off of portions of the wrap and splash molten metal. This technique is expensive and also includes fibers which are discouraged from use in some countries because the fibers are regarded as a health hazard. Other types of protective coverings include vacuum formed fiber sleeves. These coverings are expensive and include the undesirable fiber. A further protective coating involves a coating of ceramic bonded onto a steel tube. This does not outgas and there is no reaction. It is also the most expensive. Moreover, when used with thermocouples, it conducts heat into the cold junction of the thermocouple area and can damage the thermocouple, provide poor performance and afford a limited life of the thermocouple.
It has been common to use one or more cardboard sleeves or tubes to protect the sampling cartridges whether they are immersion samplers illustrated in U.S. Pat. No. 3,481,201 or a stream sampler such as shown in U.S. Pat. No. 3,996,803. Examples of refractory fiber protection is found in U.S. Pat. Nos. 4,521,639 and 3,816,183. U.S. Pat. No. 4,396,792 is a further example of a precast refractory fiber sleeve.
U.S. Pat. No. 3,455,164 shows a metal tube wrapped with a ceramic impregnated asbestos fiber.